Simulation of magnetization process and Faraday effect of magnetic bilayer films

We described ferromagnetic film and bilayer films composed of two ferromagnetic layers coupled through antiferromagnetic interfacial interaction by classical Heisenberg model and simulated their magnetization state,magnetic permeability,and Faraday effect at zero and finite temperature by using the Landau–Lifshitz–Gilbert(LLG)equation.The results indicate that in a microwave field with positive circular polarization,the ferromagnetic film has one resonance peak while the bilayer film has two resonance peaks.However,the resonance peak disappears in ferromagnetic film,and only one resonance peak emerges in bilayer film in the negative circularly polarized microwave field.When the microwave field’s frequency exceeds the film’s resonance frequency,the Faraday rotation angle of the ferromagnetic film is the greatest,and it decreases when the thickness of the two halves of the bilayer is reduced.When the microwave field’s frequency remains constant,the Faraday rotation angle fluctuates with temperature in the same manner as spontaneous magnetization does.When a DC magnetic field is applied in the direction of the anisotropic axis of the film,the Faraday rotation angle varies with the DC magnetic field and shows a similar shape of the hysteresis loop.

Magnetic diagnostics layout design for CFETR plasma equilibrium reconstruction

Plasma equilibrium reconstruction provides essential information for tokamak operation and physical analysis.An extensive and reliable set of magnetic diagnostics is required to obtain accurate plasma equilibrium.This study designs and optimizes the magnetic diagnostics layout for the reconstruction of the equilibrium of the plasma according to the scientific objectives,engineering design parameters,and limitations of the Chinese Fusion Engineering Test Reactor(CFETR).Based on the CFETR discharge simulation,magnetic measurement data are employed to reconstruct consistent plasma equilibrium parameters,and magnetic diagnostics'number and position are optimized by truncated Singular value decomposition,verifying the redundancy reliability of the magnetic diagnostics layout design.This provides a design solution for the layout of the magnetic diagnostics system required to control the plasma equilibrium of CFETR,and the developed design and optimization method can provide effective support to design magnetic diagnostics systems for future magnetic confinement fusion devices.

A Sensitivity Mapping Technique for Tensile Force and Case Depth Characterization Based on Magnetic Minor Hysteresis Loops

In the nondestructive testing and evaluation area,magnetic major hysteresis loop measurement technology are widely applied for ferromagnetic material evaluation.However the characterization ability of major hysteresis loop measurement technology greatly varies as the evaluated target properties.To solve this limitation,magnetic minor hysteresis loops,which reflect the responses of ferromagnetic material magnetization in a systematic way,is recommend.Inspired by plenty of information carried by the minor loops,the sensitivity mapping technique was developed to achieve the highest sensitivity of minor-loop parameters to the nondestructively evaluated targets.In this study,for the first time,the sensitivity mapping technique is used to measure the tensile force in a steel strand and evaluate the effective case depth in induction-hardened steel rods.The method and procedures for the sensitivity mapping technique are given before experimental detection.The obtained experimental results indicate that the linear correlation between the induced voltage(or the magnetic induction intensity)and the tensile force(or effective case depth)exists at most of the locations in the cluster of minor loops.The obtained sensitivity maps can be used to optimize the applied magnetic field(or excitation current)and the analyzed locations at the minor loops for achieving the highest sensitivity.For the purpose of tensile force measurement,it is suggested that the strand should be firstly magnetized to the near-saturation state and then restored to the remanent state.In this way,the highest sensitivity is obtained as about 15.26 mV/kN.As for the induction-hardened steel rods,the highest sensitivity of magnetic induction intensity to the effective case depth occurs under low magnetic field conditions and the absolute value of the highest sensitivity is about 0.1110 T/mm.This indicates that if the highest sensitivity is required in the case depth evaluation,the induction-hardened steel rods are only required to be weakly magnetized.The proposed sensitivity mapping technique shows the good performance in the high-sensitivity evaluation of tensile force and case depth in ferromagnetic materials and its application scope can be extended to other nondestructive detection fields.

The Positions and Number of Flux Loops and Magnetic Probes for the HT-7U Superconducting Tokamak

The plasma shape and other paremeters such as /3P, li is important for the tokamak deveice where the plasma has a non-circular cross-section of sufficient elongation. The measuered signals of magnetic probes and flux loops are used to reconstruct the plasma shape and the current profile in device operation and plasma shape feed back control system. So the number and positions of magnetic probes and flux loops provides the basis of the plasma reconstruction. This paper instroduce how to use EFIT code (equilibrium fitting code) to determine the number and positions of the magnetic probes and flux loops. The simulation result is given also.

Synthesis, Crystal Structure and Magnetic Properties of a One-dimensional Loop-like Iron(Ⅱ) Complex:[Fe(Haip)_2(H_2O)_2]_n (Haip = 5-Ammoniumisophthalato)

An iron（Ⅱ） coordination polymer, [Fe（Haip）2（H2O）2]n （1, Haip = 5-ammoniumiso- phthalato）, has been hydro/solvothermally synthesized and characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectrum and magnetic measurement. Compound 1 crystalizes in monoclinic, space group P2/c with a = 6.9874（14）, b = 9.960（2）, c = 12.894（4） A, β = 117.47（2）°, Fe（C8H6NO4）2（H2O）2, Mr = 452.16, V= 796.2（3） A3, Z = 2, Dc = 1.886 g.cm-3, p = 1.017 mm-1, F（000） = 464.0, 2.71〈0〈28.42°, R = 0.0307, wR = 0.0840 and S = 1.005. Single-crystal X-ray diffraction analysis reveals that 1 features an infinite one-dimensional loop-like chain structure and Haip ligand in 1 is of zwitterionic form. Magnetic measurement results show the dominated ferromagnetic interactions among Fe11 atoms.

Magnetic Loop Oscillation Associated with a Large Type-Ⅳμ Burst and Millisecond Spike Emission

A rare large Type Ⅳμ burst, appeared above active region NOAA/USAF 5278 was observed at Yunnan Observatory with Phoenix Ⅱ Microwave Spectrometer at three frequencies (4 00, 2 84 and 1 42 GHz) on December 16, 1988. The burst consisted of 5 main peaks with a quasiperiod of 12 5 min, on which many complex millisecond spike emissions were superimposed. Within the first main peak there were 8 secondary peaks with a quasi period of 98s (at 4 00 GHz), 72s (2 84 GHz) and 60s (1 42 GHz). A semi quantitative explanation is given for the variation of the quasi period with frequency in terms of MHD modulated oscillations in the magnetic flux tube.

Design of Magnetic Measurement System on SUNIST Spherical Tokamak

A magnetic measurement system consisting of magnetic probes and flux loops for spherical tokamak SUNIST, is uniquely designed due to the strongly shaped plasma cross section and the narrow space near the central solenoid. Plasma equilibrium reconstruction with the current filament method is performed to determine the number and positions of the magnetic probes and flux loops, as well as their design precision required.

Micromagnetic simulation of Sm–Co/α-Fe/Sm–Co trilayers with various angles between easy axes and the film plane

Hysteresis loops and energy products have been calculated systematically by a three-dimensional （3D） software OOMMF for Sm-Co/α-Fe/Sm-Co trilayers with various thicknesses and β, where β is the angle between the easy axis and the field applied perpendicular to the film plane. It is found that trilayers with a perpendicular anisotropy possess considerably larger coercivities and smaller remanences and energy products compared with those with an in-plane anisotropy. Increase of β leads to a fast decrease of the maximum energy product as well as the drop of both remanence and coercivity. Such a drop is much faster than that in the single-phased hard material, which can explain the significant discrepancy between the experiment and the theoretical energy products. Some modeling techniques have been utilized with spin check procedures performed, which yield results in good agreement with the one-dimensional （1D） analytical and experimental data, justifying our calculations. Further, the calculated nucleation fields according to the 3D calculations are larger than those based on the 1D model, whereas the corresponding coercivity is smaller, leading to more square hysteresis loops and better agreement between experimental data and the theory.

Magnetic Coupling in La_(0.67)Ca_(0.33)MnO_3/La_(0.67)Sr_(0.33)CoO_3/La_(0.67)Ca_(0.33)MnO_3 Trilayer Films

The perovskite La_(0.67)Ca_(0.33)MnO_3/La_(0.67)Sr_(0.33)CoO_3/La_(0.67)Ca_(0.33)MnO_3 trilayers were fabricated by a facing-target sputtering technique and their magnetotransport properties were investigated. The magnetoresistance is dependent on spacer thickness and dramatically decreases when La_(0.67)Sr_(0.33)CoO_3 layer is thick enough because of its short-circuiting effect. Different from La_(0.67)Ca_(0.33)MnO_3 single layer, trilayer films with thin La_(0.67)Sr_(0.33)CoO_3 spacer have the enhanced metal-semiconductor transition temperature (T_(MS)) of La_(0.67)Ca_(0.33)MnO_3 layers. The magnetic coercivity H_C shows a nonmonotonic behavior with changing the spacer layer thickness at 230 K. The waist-like hysteresis indicates that there is an indirect exchange coupling between the top and bottom La_(0.67)Ca_(0.33)MnO_3 layers across the spacer La_(0.67)Sr_(0.33)CoO_3 layer.

Observation of Magnetic Domain Structures of Magnetic Thin Films by the Lorentz Electron Microscopy

The microstructure change in thin NiFe/Cu/NiFe films during the magnetization process was observed by the Lorentz electronmicroscopy. TWo types of films were prepared: (1) one NiFe layer with anisotropy and the other layer without, and (2) both NiFe layershave anisotropy normal each other. The domain wall migration and magnetization rotation processes in each of NiFe layers could be observed separately. The presence of magnetic anisotropy in the magnetic layer effectively controls the behavior of magnetic domains. Theinteraction between the two NiFe layers of the film could be observed not so strong in the present experiment.

Study and Characterization of Soft Magnetic Properties of Fe_73.5Cu₁Nb3Si_13.5B₉Magnetic Ribbon Prepared by Rapid Quenching Method

Nanocrystalline Fe-based alloys offer a new opportunity for tailoring soft magnetic materials. Nanocrystalline alloy in the form of ribbon with the composition of Fe73.5Cu1Nb3Si13.5B9 was prepared by rapid quenching method for soft magnetic properties analysis. The rapidly quenched alloy has been annealed in a controlled way in the temperature range 490℃ to 680℃ and annealing time 1 min to 60 min. The study of the structural parameters has been investigated by means of XRD analysis. Magnetic properties were analyzed by measuring B-H loop and frequency dependence of initial permeability. Enhanced value of initial permeability by two orders of magnitude and very low value of relative loss factor of the order of 10–3 has been observed with the variation of annealing temperature and time. The initial permeability for the optimum annealed sample has been found 23,064 as compared with 360 for its amorphous counterpart. The initial permeability spectra show dispersion around 100 kHz. Magnetic hysteresis has been investigated by measuring B-H loops at various magnetic fields for different annealing temperature and time. The coercivity and remanence has been found to decrease significantly for optimized annealed condition compared to as-cast state. The core loss of the samples decreases with the annealing time which indicates the good magnetic property of soft magnetic materials.

Asymmetric Magnetization Reversal Probed by Recoil Loop Measurements in an Exchange Biased La0.67Sr0.33MnO3/La0.33Ca0.67MnO3 Bilayer Film

We exploit the recoil loop measurements to study La0.07 Sr0.33 Mn O3/La0.33 Ca0.67 Mn O3 bilayer film. the asymmetric magnetization reversal in an exchange-biased It is found that the recoil curve encloses a marked area only in the second quadrant of the hysteresis loop, and the recoil susceptibility in the descending branch of the major loop is evidently higher than that in the ascending branch. The study indicates that the exchange anisotropy of a unidirectional nature and an orientation deviated from the easy axis of the ferromagnetic layer plays a crucial role in creating the reversal asymmetry.

Factors Affecting the Squareness of Hysteresis Loops of Sintered NdFeB Magnets

Investigation into the magnets with different squareness of hysteresis loop(SHL) reveals that the microstructure of sintered NdFeB magnets has great effects on the SHL of the magnets. The abnormal grain growth deteriorates the SHL seriously. The shape of the grain and the grain boundary affect the intensity of demagnetization field, and consequently on the SHL. The added elements have effects on the phase structures and distributions in the magnets, which influences the uniform of demagnetization field.

Magnetic properties of a mixed spin-3/2 and spin-2 Ising octahedral chain

Using an effective field theory with correlations, magnetic properties of an octahedral chain described by a mixed spin Ising model are investigated. Unique phenomena such as multiple hysteresis loops, saturation magnetization, and reverse flip of the magnetization plateaus occur when certain typical parameters are applied. These results may be helpful to further investigate the magnetic properties of one-dimensional systems and could potentially be utilized in the design of spin devices.

Hysteresis of the Magnetic Particle in a Dipolar Ising Model

Zero-temperature Monte Carlo simulations are used to investigate the hysteresis of a magnetic particle ina dipolarIsing model. The magnetic particle is described in a system of permanent dipoles, and the dipoles are locatedin a cubic lattice site. The effects of the shape and the size of the particle on the hysteresis loop at zero temperatureare obtained. For strong exchange interactions, the shapes of magnetic hysteresis loops approach rectangle. For weakexchange interactions, the effects of the size and the shape of the particle on the loops are more remarkable than thoseof strong exchange interactions case. The slope of the hysteresis loop decreases with the increase of the ratio of thesemi major axis to the semi minor axis of the ellipsoidal magnetic particle, and there is an increase of the slope of thehysteresis with the decrease of the size of the magnetic particle. The effects of the shape and size of the particle on thecoercive force at zero temperature are also investigated.

Structural, Magnetic and Dielectric Properties of Fe-Co Co-Doped Ba_0.9Sr_0.1TiO₃Prepared by Sol Gel Technique

The structural, dielectric and magnetic properties of pure and Fe-Co co-doped Ba0.9Sr0.1TiO3, (Ba(1-x)SrxTiO3, where (x = 0.10) and (Ba0.9Sr0.1Ti(1-x-y)FexCoyO3), where (x = 0.1, y = 0) and (x = 0 and y = 0.10) and (x = 0.5, y = 0.5) in powder form, abbreviated as (BST) and (BST10FO), (BST10CO) and (BST5F5CO), respectively were prepared by a modified sol gel technique. Crystallization, surface morphology and electrical behavior of BST are improved by Fe3+ and Co2+ ions with optimized grain size. Phase identification by using X-ray diffraction and surface morphology will be studied by using transmission electron microscope (TEM) and scanning electron microscope imaging (SEM). Phase identification by using X-ray diffraction and surface morphology evaluation by using transmission electron microscope (TEM) and scanning electron microscope imaging (SEM) will be studied. The nano-scale presence and the formation of the tetragonal perovskite phase as well as the crystallinity were detected using the mentioned techniques. The dielectric properties of the prepared samples have been investigated as a function of temperature and frequency. The dielectric measurements are carried out in the frequency range of 42 Hz - 1 MHz, at temperature ranging between 25°C and 250°C. The results showed an abrupt decrease in the dielectric permittivity by increasing the frequency range. The magnetic hysteresis loop confirmed enhancement in the magnetization properties by co-doping with Fe3+-Co2+ ions. An increase in the saturation of the magnetization at room temperature was detected by decreasing the crystallite sizes of the prepared samples.

范德华铁磁体Fe_(3)GeTe_(2)反常霍尔效应调控研究

【目的】磁性材料的本征磁矩可以引发反常霍尔效应,显著降低霍尔电阻,从而改善微纳电子器件热损弊端。二维范德华磁性材料在原子级厚度上展现了出色的铁磁特性与输运性能,可用于制备下一代低维自旋电子器件,在低功耗自旋电子学、量子计算和光通信领域具有巨大的潜力。【方法】研究了块体Fe_(3)GeTe_(2)(FGT)的铁磁性和磁各向异性,制备了基于FGT的标准霍尔器件,并详细研究了不同温度和外加磁场方向下FGT纳米片的磁电输运性能。【结果】结果显示,块体FGT在低于居里温度(Tc=165 K)时,具有显著的面外磁易轴(H//c)。零磁场时,存在0.764Ω的反常霍尔电阻(20 K),并且,在140 K时减小到0.332Ω,证明了FGT具有随温度调控的反常霍尔效应;随着外加磁场方向改变,磁滞回环由接近矩形逐渐转变为扁平菱形,表明FGT磁化方向已由面外转变为面内,进一步验证了FGT具有本征的面外磁各向异性。最后,我们还计算了大磁场下(-6 T~6 T)FGT的载流子浓度(20 K时为2.5×10^(22)cm^(-3))和迁移率(20 K时为13.3 cm^(2)/(V·s))。

基于高阶滑模观测器和改进型PLL的感应电机无传感器控制

针对传统一阶滑模观测器的感应电机无传感器控制方法存在的固有抖振问题,本文提出了一种基于高阶滑模观测器和改进型锁相环的感应电机无传感器控制方法。首先,提出了一种自适应非奇异快速终端滑模磁链观测器,该观测器可以使得系统全局快速收敛且抖振减小,同时有效提升了系统的鲁棒性;其次,将超螺旋算法引入传统的PLL中,采用了一种基于三阶超螺旋算法的改进型锁相环,进一步提升了转速估计的精度,有效抑制了转速抖振;最后,仿真结果表明,所提控制策略能有效提升系统鲁棒性,抑制估计转速的抖振,证明了所提方法的有效性和可行性。

Experimental study on magnetomechanical coupling effect of Q235 steel tubular member specimens

The magnetomechanical coupling tests were performed on Q235 steel tubular model specimens in NIM-2000HF magnetomechanical coupling equipment. The hysteresis loops were obtained in different magnetic fields and stresses. The magnetization curves were also achieved at different stresses. The influence of applied stresses on the hysteresis loops was investigated. The stress sensitive region and linear stress sensitive region of magnetic induction are determined for the model specimen according to the experimental data. The linear dependence relation of magnetic induction versus applied stresses is established, and the optimum magnetic field is determined in the stress sensitive range of magnetic induction, which builds a basis for nondestructive testing (NDT) of stress with the total magnetic flux for steel structure.

Vector control of permanent magnet synchronous motor based on dynamic matrix control

Aiming at the control problem of strongly nonlinear and coupled permanent magnet synchronous motor(PMSM)oil rig,this paper presents a predictive control method based on dynamic matrix model.In this method,the dynamic matrix algorithm using multistep prediction technique is applied to the speed loop control of the motor vector control.And its control effect is compared with the traditional proportional integral(PI)control of the motor.By comparing the initial dynamic response and the steady-state recovery under load interference of the two methods,it is shown that the dynamic response and the robustness of the motor controlled by the new method is better than that controlled by conventional PI method.And the feasibility of new control in the application of PMSM oil rig is verified.